Steam turbine overspeed protection method and system

ABSTRACT

A method and system is disclosed for generating a steam turbine overspeed control system fault alert. The method can include providing an overspeed control system with a control valve configured and located to adjust a speed of the steam turbine, the control valve having a control position. The method can also include monitoring the control position of the control valve and detecting a deloading event. Upon detection of a deloading event, a control system fault alert is generated when the control valve does not achieve a predefined control position within a predefined time from the deloading event.

RELATED APPLICATION(S)

This application claims priority under 35 U.S.C. §119 to European Patent Application No. 10195773.6 filed in Europe on Dec. 17, 2010, the entire content of which is hereby incorporated by reference in its entirety.

FIELD

The present disclosure relates to steam turbine overspeed protection, for example, to control overspeed in a case of a steam turbine unloading event.

BACKGROUND INFORMATION

Known steam turbines can be equipped with trip systems that can prevent steam turbine speed from exceeding a defined overspeed value. Overspeed, which may occur following steam turbine unloading events, can be the result of a transient rotational speed spike caused by delay in system dynamic and control system lag as the turbine's control system assumes new control positions. The event may be an undetectable load shedding event, such as a sudden drop in power demand, or a detectable event, such as the opening of a power breaker.

Power grid codes can pre-define operating bands that limit operation above nominal speeds. The overspeed trip setpoint can be determined by adding the expected overspeed resulting from a load shedding event to a peak speed within an operating band.

Following an unloading event, it is desirable that the power plant is available to be brought on line as soon as possible. Because it can take time to bring a steam turbine on line after a trip, it is desirable to limit the number of trips.

Machine damage can occur below a maximum rotor designed speed if, for example, resonance build-up occurs within the blading. While damaging resonance build-up in the blading can occur if a particular system specific speed is sustained and so may not occur during transient overspeed events such as unloading events, it is desirable to minimise the exposure of blades to speeds outside the normal operating band in order to reduce potential blade stressing.

SUMMARY

A method is disclosed for generating a steam turbine overspeed control system fault alert comprising: providing an overspeed control system with a control valve configured and located to adjust a speed of the steam turbine, the control valve having a control position; monitoring the control position of the control valve; detecting a deloading event; and generating a control system fault alert when the control valve does not achieve a predefined control position within a predefined time from the deloading event.

An overspeed control system is disclosed for generating a steam turbine overspeed fault alert, comprising: a control valve configured and located to adjust a speed of the steam turbine, the control valve having a control position; a monitor for monitoring the control position of the control valve; a detector for detecting a deloading event; and a controller for generating a control system fault alert when the control valve does not achieve a predefined control position within a predefined time from the deloading event.

A power plant is disclosed comprising: a steam turbine having a generator and a power breaker; and an overspeed control system including: a control valve configured and located to adjust a speed of the steam turbine, the control valve having a control position; a monitor for monitoring the control position of the control valve; a detector for detecting a deloading event; and a controller for generating a control system fault alert when the control valve does not achieve a predefined control position within a predefined time from the deloading event.

BRIEF DESCRIPTION OF THE DRAWINGS

An exemplary embodiment of the present disclosure is described more fully hereinafter with reference to the accompanying drawing, in which:

FIG. 1 is a schematic of an exemplary embodiment of a steam plant that includes an exemplary embodiment of an overspeed control system.

DETAILED DESCRIPTION

The disclosure relates to providing an early warning steam turbine overspeed control system fault alert before a critical overspeed is reached.

An exemplary method for generating a steam turbine overspeed control system fault alert according to an exemplary embodiment includes providing an overspeed control system with a control valve that is configured and located to adjust the speed of the steam turbine wherein the control valve has a control position. The method includes monitoring a control position of the control valve, detecting a deloading event, and generating a control system fault alert when (i.e., if, or whenever) the control valve does not achieve a predefined control position within a predefined time from the deloading event.

In an exemplary embodiment, the deloading event can be a predefined steam turbine speed. In an exemplary embodiment, the predefined time can be substantially zero (e.g., within 5 seconds, such as 1 second).

In an exemplary embodiment in which the steam turbine is a component of a power plant, the detecting can include detecting the opening of a power breaker of the power plant.

An exemplary embodiment can include an overspeed control system with a control valve that is configured and located to adjust the speed of the steam turbine wherein the control valve has a control position. The overspeed control system can be configured to monitor the control position of the control valve, detect a deloading event, and generate a control system fault alert if the control valve does not achieve a predefined control position within a predefined time from the deloading event.

Exemplary embodiments of the present disclosure are now described with references to the drawing. In the following description, for purposes of explanation, numerous specific details are set forth to provide a thorough understanding of the disclosure. However, the present disclosure may be practiced without these specific details, and is not limited to the exemplary embodiments disclosed herein.

FIG. 1 shows exemplary embodiments of a power plant 10 and a steam turbine 15. The power plant 10 includes an exemplary embodiment of an overspeed control system 20 for preventing or at least minimising overspeed of a steam turbine 15 in both normal and upset conditions. The power plant 10 can include a steam turbine 15 with a generator 16. Between the generator 16 and the grid is a breaker 18. The control system 20 has a controller 26 for monitoring control inputs, calculating control parameters and distributing these control parameters to control elements such as control valves 22.

An exemplary embodiment of the disclosure provides a method for generating a fault alert that provides an alert that the steam turbine overspeed control system 20 has not taken the expected action and therefore may not be capable of preventing overspeed of the steam turbine 15. Overspeed can be defined as steam turbine shaft speed above the operating speed band or operating design speed of the steam turbine 15.

The exemplary method includes providing an overspeed control system 20 with a control valve 22 that is configured and located to adjust the speed of the steam turbine 15. This can be achieved, for example, by a control valve 22 located in the feed line to the steam turbine 15, as shown in FIG. 1. In another exemplary embodiment a steam turbine interstage vent valve can be located in an interstage vent line of the steam turbine 15.

The exemplary method includes measuring a control position of the exemplary control valve 22. In an exemplary embodiment, monitoring involves monitoring the control valve position signal generated by the controller 26. In another exemplary embodiment, the monitoring involves monitoring the actual control position of the control valve 22 using known methods.

The exemplary method can include detecting a deloading event. In an exemplary embodiment, the deloading event is a predefined steam turbine speed. This can be a steam turbine speed at the top end of the operating band and/or operating design speed window. In another exemplary embodiment, the deloading event, when the steam turbine 15 is a component of a power plant 10, can be the opening of a power breaker 18 of the power plant 10.

The exemplary method can include generating a control system fault alert if the control valve 22 does not achieve a predefined control position within a predefined time from the deloading event. The logic behind the fault alert is that, following a deloading event 12, the overspeed control system 20 is configured to send a predictable signal to the control valve 22 that will, in turn, respond to this signal in a predictable way. If the predictable action, for example, sending of a control signal or achieving a control position, is not achieved, the likely cause is an overspeed control system fault. This exemplary fault may be due to the failure of any part of the overspeed control system 20, including but not limited to, the detection of the deloading event, the calculation of the control response, the signal to the control valve 22 or the control valve 22 itself.

An exemplary embodiment provides an overspeed control system 20 that is configured to generate an overspeed control system fault alert. The overspeed control system 20 includes a control valve 22 that is configured and located to adjust the speed of the steam turbine 15. The control valve 22 has a control position and a position sensor for monitoring the control position. The overspeed control system 20 further has a sensor for detecting a deloading event. An example of this can be, for example, a power breaker status monitor. The overspeed control system 20 includes a control system for generating a control system fault alert if the control valve 22 does not achieve a predefined control position within a predefined time from the deloading event. This can be, for example, a control logic located within a controller 26 or a microprocessor coupled to a memory.

Thus, it will be appreciated by those skilled in the art that the present invention can be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The presently disclosed embodiments are therefore considered in all respects to be illustrative and not restricted. The scope of the invention is indicated by the appended claims rather than the foregoing description and all changes that come within the meaning and range and equivalence thereof are intended to be embraced therein.

REFERENCE NUMBERS

-   10 Power plant -   15 Steam turbine -   16 Generator -   18 Power breaker -   20 Overspeed control system -   22 Control valve -   26 Controller 

1. A method for generating a steam turbine overspeed control system fault alert comprising: providing an overspeed control system with a control valve configured and located to adjust a speed of the steam turbine, the control valve having a control position; monitoring the control position of the control valve; detecting a deloading event; and generating a control system fault alert when the control valve does not achieve a predefined control position within a predefined time from the deloading event.
 2. The method of claim 1 wherein the deloading event is a predefined steam turbine speed.
 3. The method of claim 2 wherein the predefined time is substantially zero.
 4. The method of claim 2 wherein the steam turbine is a component of a power plant with a generator, wherein the detecting a deloading event includes detecting the opening of a power breaker of the power plant.
 5. An overspeed control system for generating a steam turbine overspeed fault alert, comprising: a control valve configured and located to adjust a speed of the steam turbine, the control valve having a control position; a monitor for monitoring the control position of the control valve; a detector for detecting a deloading event; and a controller for generating a control system fault alert when the control valve does not achieve a predefined control position within a predefined time from the deloading event.
 6. The overspeed control system of claim 4, wherein the deloading event is a predefined steam turbine speed.
 7. The overspeed control system of claim 4, wherein the predefined time is zero.
 8. A power plant comprising: a steam turbine having a generator and a power breaker; and an overspeed control system including: a control valve configured and located to adjust a speed of the steam turbine, the control valve having a control position; a monitor for monitoring the control position of the control valve; a detector for detecting a deloading event; and a controller for generating a control system fault alert when the control valve does not achieve a predefined control position within a predefined time from the deloading event.
 9. The power plant of claim 8, wherein the deloading event is a predefined steam turbine speed.
 10. The power plant of claim 8, wherein the detecting a deloading event includes detecting the opening of the power breaker of the power plant
 11. The power plant of claim 8, wherein the predefined time is substantially zero. 